Multicomponent self-bulking fibers

ABSTRACT

The present invention provides multicomponent fibers designed to curl in response to external stimuli such as heat or moisture. The multicomponent fiber can have cross-sectional area comprising the first polymer component and the second polymer component, wherein the first polymer component and the second polymer component are configured in an eccentric sheath/core arrangement and wherein the core component has a non-circular shape. Also, the multicomponent fiber has a first cross-sectional center of mass and a cross-sectional periphery, the core component has a second cross-sectional center of mass; and the second cross-sectional center of mass is positioned from about 20 percent to about 70 percent of the distance from the first cross-sectional center of mass to a point on the cross-sectional periphery. Furthermore, the present disclosure provides a fabric including a plurality of multicomponent fibers designed to curl in response to external stimuli such as heat or moisture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No. 62/257,906, filed on Nov. 20, 2015, which is hereby incorporated in its entirety by reference in this application.

FIELD OF INVENTION

The present disclosure relates to a multicomponent fiber. In particular, the fiber can exhibit useful self-bulking characteristic in response to external stimuli.

BACKGROUND

Synthetic fibers are widely used in a number of diverse applications to provide stronger, thinner, and lighter weight products. Synthetic fibers are suitable for use in a variety of materials, including woven fabrics, nonwoven fabrics, and yarns.

Various embodiments of multicomponent fibers known in the art include eccentric sheath/core fibers with circular cross-section cores. These fibers typically are designed to curl irreversibly in response to heat, by exploiting the difference in shrinkage between the two polymers. A more recent development is a fiber that curls in response to changes in humidity. See, e.g., U.S. Pat. Appl. Pub. Nos. 2011/0092121 to Kapsali and 2015/0140886 to Kapsali, each of which is herein incorporated by reference in its entirety.

Various commercial products comprising multicomponent fibers are designed to respond to humidity or moisture. For example, various articles of apparel are designed to adjust to humidity or moisture (e.g., as a result of sweat) in order to adjust the breathability of one or more fabrics in the apparel, thereby improving the comfort of the apparel.

It is desirable to provide a multicomponent self-bulking fiber (i.e., a fiber that curls in response to external stimuli such as heat or moisture), wherein the degree of bulking or curling can be controlled while still maintaining fiber integrity and functionality.

SUMMARY OF THE INVENTION

The present invention provides multicomponent fibers that are designed to curl in response to external stimuli such as heat or moisture. The multicomponent fibers of the present invention can have a sheath/core arrangement and can comprise a sheath component comprising a first polymer component, and a core component comprising a second polymer component, wherein the core component has a first axis that is substantially perpendicular to a second axis, and wherein the first axis is longer than the second axis such that the core component has a non-circular shape. In addition, the multicomponent fiber can have a first cross-sectional center of mass and a cross-sectional periphery, the core component can have a second cross-sectional center of mass, and the second cross-sectional center of mass can be positioned from about 20 percent to about 70 percent, or from about 30 percent to about 40 percent of the distance from the first cross-sectional center of mass to a point on the cross-sectional periphery. The multicomponent fiber can be selected from the group consisting of continuous filaments, staple fibers, electrospun fibers, spunbond, and meltblown fibers, for example.

In various embodiments of the present invention, the first polymer component can be selected from the group consisting of a polyolefin, a polyester, a polyamide, a cellulose derivative, a polyaramid, an acetal, fluoropolymers, copolymers and terpolymers thereof, and mixtures or blends thereof. In certain embodiments, the first polymer component can be a polyamide.

In various embodiments of the present invention, the second polymer component can be selected from the group consisting of a polyolefin, a polyester, a polyamide, a cellulose derivative, a polyaramid, an acetal, fluoropolymers, copolymers and terpolymers thereof, and mixtures or blends thereof. In certain embodiments, the second polymer component can be a polyolefin.

In various embodiments of the present invention, the core component can be non-circular in shape. Preferably, the non-circular cross-sectional shape can be substantially elongated. In one or more embodiments, the core can have a first curved shape proximal the outer periphery of the fiber and can have a second, different curved shape proximal the center of mass of the fiber. For example, the core can have a substantially circular curve facing the outer periphery of a cross-section of the multicomponent fiber and a substantially elliptical curve connected to the substantially circular curve, wherein the substantially elliptical curve can define the side of the core component that is facing the interior of the multicomponent fiber (e.g., facing opposite the circular curved face of the core component). In some embodiments of the present invention, the core component can be substantially elliptically shaped, substantially D-shaped, or substantially crescent-shaped. The length of a first axis of the core component can be about 1.5 to about 2.0 times the length of a second axis of the core component, for example. In certain embodiments, the multicomponent fiber can have a cross-sectional area comprising about a 40:60 to about a 90:10 ratio of the sheath component to the core component. In some embodiments, the multicomponent fiber has a cross-sectional area comprising about a 50:50 to about a 75:25 ratio of the sheath component to the core component.

The present invention also provides a fabric comprising a plurality of multicomponent fibers as described herein. A method of forming a nonwoven fabric is also provided herein, wherein the method comprises providing a plurality of multicomponent fibers as described herein, and bonding the plurality of multicomponent fibers.

The fibers disclosed herein further can be used in the manufacture of further materials. For example, the present disclosure also encompasses spun yarns comprising the present fibers. In further, non-limiting examples, materials that can comprise the present fibers include plugs, tows, waddings, ropes, cords, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 is a transverse cross sectional view of an exemplary sheath/core multicomponent fiber of the invention;

FIG. 2 is a transverse cross sectional view of a second exemplary sheath/core multicomponent fiber of the invention;

FIG. 3 is a transverse cross sectional view of an exemplary sheath/core multicomponent fiber of the invention;

FIG. 4 is a transverse cross sectional view of an exemplary core component of a multicomponent fiber of the invention; and

FIG. 5 is a transverse cross sectional view of a multicomponent fiber illustrating the cross-sectional area in which the center of mass of a core component may be positioned according to one or more embodiments of the invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used in this specification and the claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Reference to “dry weight percent” or “dry weight basis” refers to weight on the basis of dry ingredients (i.e., all ingredients except water).

The present disclosure provides a multicomponent thermoplastic self-bulking fiber (i.e., a fiber that curls in response to external stimuli such as heat or moisture), wherein the degree of bulking or curling can be controlled while still maintaining fiber integrity and functionality. As used herein, “self-bulking” refers a fiber (or a fabric comprising a plurality of fibers) that responds to an activation such as a change in moisture or heat. For example, in various embodiments of the present invention, a fabric is provided that comprises an activatable element (e.g., fibers that will respond to activations such as a change in humidity by changing shape or deforming). In some embodiments, the activatable elements can change shape (e.g., twist or curl) and can thereby allow for large spaces between the fibers of the fabric. As such, moisture and/or heat that is trapped by the fabric can escape. In contrast, when the activatable elements are not activated (e.g., the fabric is dry), the activatable elements can fill gaps between fibers of the fabric.

The multicomponent fiber can comprise a first polymer component comprising a first thermoplastic material and a second polymer component comprising a second thermoplastic material, wherein the first polymer component comprises at least a portion of an exposed surface of the multicomponent fiber. In some embodiments as used herein, an exposed surface can refer to at least a portion of a circumference of a cross-sectional area of the multicomponent fiber. In further embodiments, an exposed surface can comprise any area of the fiber surface that is exposed to ambient surroundings.

The term “fiber” as used herein means both fibers of finite length, such as conventional staple fibers and nanofibers, as well as substantially continuous structures, such as continuous filaments, unless otherwise indicated. The fibers of the invention particularly can be multicomponent fibers. The fibers can have a substantially round or circular cross section or non-circular cross sections (for example, oval, rectangular, multi-lobed, and the like).

As used herein, the term “multicomponent fibers” includes staple and continuous fibers prepared from two or more polymers present in discrete structured domains in the fiber, as opposed to blends where the domains tend to be dispersed, random or unstructured. For purposes of illustration only, the present subject matter is generally described in terms of an exemplary bicomponent fiber comprising two polymer components. However, it should be understood that the scope of the present invention is meant to include fibers with two or more structured components and is not limited to the exemplary bicomponent fibers described below. Although the invention is not limited to two components, the terms first component and second component are used throughout for the ease of describing the invention.

In general, the polymer components are arranged in substantially constantly positioned distinct zones across the cross section of the multicomponent fiber and extend continuously along the length of the multicomponent fiber. Both the shape of the fiber and the configuration of the components therein will depend upon the equipment that is used in the preparation of the fiber, the process conditions, and the melt viscosities of the various components. A wide variety of fiber configurations are possible in the present invention. The cross section of the multicomponent fiber can particularly be circular, since the equipment typically used in the production of multicomponent synthetic fibers often produces fibers with a substantially circular cross section; however, other cross sections are encompassed. The configuration of the first and second components in a fiber of circular cross section can be either concentric or eccentric, the latter configuration sometimes being known as a “modified side-by-side” or an “eccentric” multicomponent fiber.

FIGS. 1-3 are cross-sectional views of exemplary multicomponent fibers of the present invention, designated generally as 10. Multicomponent fiber 10 is a sheath/core fiber that includes at least two structured polymer components: (i) an outer sheath component comprising a first polymer component 2; and (ii) an inner core component comprising a second polymer component 4.

The core (formed of the second polymer component 4) can be concentric, or at least approximately centered in the middle of the sheath component. A concentric configuration is characterized by the sheath component having a substantially uniform thickness so that the core component lies approximately in the center of the fiber. Concentric sheath/core fibers can be defined as fibers in which the center of the core component is biased by no more than about 0 to about 20 percent, preferably no more than about 0 to about 10 percent, based on the diameter of the sheath/core multicomponent fiber, from the center of the sheath component. In some embodiments, the fiber can have a modified concentric configuration wherein the core component lies approximately in the center of the fiber, however, due to a non-uniform cross-sectional area of the core component, the thickness of the sheath component surrounding the core component can vary slightly.

Alternatively, the core can be eccentric. As illustrated in FIGS. 1-3, the eccentric sheath/core fiber 10 includes a core (formed of the second polymer component 4) eccentrically located within the outer sheath (formed of the first polymer component 2). In an eccentric configuration the core component does not lie in the center of the fiber and therefore, the thickness of the sheath component surrounding the core component varies.

As illustrated in FIG. 3, for example, a multicomponent fiber can have a cross-sectional center of mass 6 and a core component can have a cross-sectional center of mass 8. The core component cross-sectional center of mass 8 can be positioned along a line A extending from the multicomponent component fiber cross-sectional center of mass 6 to a point 5 located on the multicomponent fiber's cross-sectional periphery. Line A can be perpendicular to the multicomponent fiber's cross-sectional periphery. For example, tangent line B in FIG. 3 is perpendicular to line A.

In various embodiments of an eccentric sheath/core fiber configuration, the cross-sectional center of mass of the core component 8 can be positioned from about 20% to about 70%, about 25% to about 60%, about 30% to about 50%, or about 30% to about 40% of the distance from the fiber's cross-sectional center of mass 6 to a point 5 on the fiber's cross-sectional periphery and on a line perpendicular to the cross-sectional periphery. Accordingly, and as illustrated in FIG. 5, for example, the cross-sectional center of mass of the core component 8 can be positioned anywhere within ring 12, which defines an area from about 20% to about 70% the length of line A, as measured from the multicomponent fiber's cross-sectional center of mass 6 to the multicomponent fiber's cross-sectional periphery.

In various embodiments of the present invention and as illustrated in FIGS. 3 and 4, the core component is not circular in shape, but instead can have a first axis L1 and a second axis L2, with the first axis L2 at least nominally perpendicular to the aforementioned line A from the multicomponent fiber's cross-sectional center of mass 6 and perpendicular to the cross-sectional periphery. The second axis L2 can be at least nominally on the line A extending from the fiber's cross-sectional center of mass 6 to its cross-sectional periphery. Thus, the core may have a substantially elliptical shape, or a nominally “banana-like” shape (e.g., FIG. 1), or a nominally “D” shape (with the curved surface nearest the fiber's periphery but still fully encapsulated by the sheath) (e.g., FIG. 2), or any similar non-standard shape. In various embodiments, the core component can have a first axis with a length about 1.1 to about 3.0, or about 1.3 to about 2.8, or about 1.5 to about 2.0 times the length of a second axis of the core component. In some embodiments, the core component can have a second axis with a length about 1.1 to about 3.0, or about 1.3 to about 2.8, or about 1.5 to about 2.0 times the length of a first axis of the core component, such that the core component is a shorter, broader shape.

Several advantages have been discovered for a non-circular core component. For example, in applications for self-bulking fibers (which curl into a nominally helical shape in response to external stimuli such as heat or moisture), the degree of curling or bulking typically depends on the degree of separation of the center of mass of the eccentric core from the center of mass of the fiber. A non-circular cross section of the core component can provide a greater separation of the centers of mass than prior art circular-core cross sections. A maximum separation of the two components can be achieved in a side-by-side fiber cross section, but a side-by-side cross section can only be used in cases where the two polymer components have sufficient adhesion to prevent them from splitting apart in processing or in the application of the multicomponent fiber. The cross section of the present invention maintains full encapsulation of the core by the sheath in order to maintain fiber integrity and functionality in cases where the two polymers do not have sufficient adhesion to prevent separation in processing or in the application of the multicomponent fiber.

Various embodiments of the multicomponent fiber have a cross-sectional area comprising the sheath component (first polymer component) and the core component (second polymer component) in about a 50:50 to about a 75:25 ratio. In some embodiments, the ratio of the cross-sectional area of the sheath component to the cross-sectional area of the core component is about a 40:60 to about a 90:10 ratio, about a 50:50 to about a 80:20 ratio, or about a 60:40 to about a 75:25 ratio.

In various embodiments of the multicomponent fiber described herein, the polymer components of the multicomponent fiber can be formed of the same or different polymers. As used herein, the “same” polymer refers to polymer components having an identical or similar chemical formula; however, each polymer component can differ with respect to their ability to flow at a target bonding temperature. The ability of a polymer component to flow at a temperature is related to crystallinity, molecular weight, and the possible presence of plasticizers, as well as the chemical composition of the polymer. Furthermore, each polymer component can differ with respect to their response to stimuli which initiates curling of the polymer component (e.g., moisture, heat, etc.). The difference in the response of the two polymer components can create different levels of swelling (e.g., in response to moisture) or shrinkage (e.g., in response to heat), which then promotes the curling of the multicomponent fibers.

A fiber according to the present disclosure can comprise one or more polymers selected from any of the types of polymers known in the art that are capable of being formed into fibers, including polyolefins, polyesters, polyamides and the like. Examples of suitable polymers include, without limitation, polyolefins including polypropylene, polyethylene, polybutene, and polymethyl pentene (PMP), polyamides including nylon, such as nylon 6 and nylon 6,6, polyacrylates, polystyrenes, polyurethanes, acetal resins, polyethylene vinyl alcohol, polyesters including aromatic polyesters, such as polyethylene terephthalate, polyethylene naphthalate, polytrimethylene terephthalate, poly(1,4-cyclohexylene dimethylene terephthalate) (PCT), polyphenylene sulfide, thermoplastic elastomers, polyacrylonitrile, cellulose derivatives, polyaramids, acetals, fluoropolymers, copolymers and terpolymers thereof and mixtures or blends thereof.

Further examples of aromatic polyesters include (1) polyesters of alkylene glycols having 2-10 carbon atoms and aromatic diacids; (2) polyalkylene naphthalates, which are polyesters of 2,6-naphthalenedicarboxylic acid and alkylene glycols, as for example polyethylene naphthalate; and (3) polyesters derived from 1,4-cyclohexanedimethanol and terephthalic acid, as for example polycyclohexane terephthalate. Exemplary polyalkylene terephthalates include without limitation, polyethylene terephthalate (also PET) and polybutylene terephthalate.

In some embodiments, one or more polymers of the multicomponent fiber can comprise an aliphatic polyester. Examples of aliphatic polyesters which may be useful in the present invention include, without limitation, fiber forming polymers formed from (1) a combination of glycol (e.g., ethylene, glycol, propylene glycol, butylene glycol, hexanediol, octanediol or decanediol) or an oligomer of ethylene glycol (e.g., diethylene glycol or triethylene glycol) with an aliphatic dicarboxylic acid (e.g., succinic acid, adipic acid, hexanedicarboxylic acid or decaneolicarboxylic acid) or (2) the self condensation of hydroxy carboxylic acids other than polylactic acid, such as polyhydroxy butyrate, polyethylene adipate, polybutylene adipate, polyhexane adipate, and copolymers containing them. Examples of aliphatic polyesters include, but are not limited to, polyglycolide or polyglycolic acid (PGA), polylactide or polylactic acid (PLA), polycaprolactone (PCL), polyethylene adipate (PEA), polyhydroxyalkonoate (PHA), polyhydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and polylactide-co-glycolide.

In various embodiments of the present invention, the sheath component (first polymer component) of the multicomponent fiber can comprise a polyamide. In some embodiments, the polyamide can be selected from the group consisting of nylon (e.g., nylon 6 and nylon 6,6), polyacrylates, polystyrenes, polyurethanes, acetal resins, polyethylene vinyl alcohol and combinations thereof. In various embodiments of the present invention, the core component (second polymer component) of the multicomponent fiber can comprise a polyolefin. In some embodiments, the polyolefin can be selected from the group consisting of polypropylene, polyethylene, polybutene, polymethyl pentene (PMP), and combinations thereof.

As mentioned above, for fibers that curl in response to heat, a critical property of the polymer components can be shrinkage rate, which is affected by polymer chemistry, molecular weight, orientation, crystallinity, and in some cases, degree of moisture absorption. In cases where the two polymer components are chemically substantially identical, molecular weight can be a critical characteristic for fibers that curl in response to heat. In the case of fibers that curl in response to moisture, a critical characteristic can be the degree to which one polymer swells in response to moisture as compared to the degree to which the second polymer component swells in response to moisture. The degree of swell in a polymer component can often be related to the level of moisture absorption of the polymer component, which is sometimes referred to as “regain.” Various polymers have moisture regains from zero to about 25 percent by weight, at 70 degrees F. and 95% humidity. Fiber swelling, as measured by increase in diameter, can be from zero (PP) to about 50 percent (e.g., some rayons). In various embodiments, the core polymer component can have about a zero to about a 5 percent moisture regain. This can correspond to about a zero percent increase in diameter, for example. In various embodiments, the sheath polymer component can have about a 5 percent to about a 15 percent moisture regain. This can correspond to about a 5 percent increase in diameter for the sheath component, for example. In a preferred embodiment, the core component can have about a zero percent moisture regain and the sheath component can have about a 9 percent moisture regain. A larger swell in the sheath could be desirable, but the polymers that typically deliver this amount of swell can present problems in processing or other property deficiencies.

In a preferred embodiment, the multicomponent fiber is an eccentric sheath/core staple fiber comprising a polypropylene core component (i.e., the second polymer component) and a nylon 6 sheath component (i.e., the first polymer component). The multicomponent fiber can have a sheath to core cross-sectional area ratio of between about 50:50 and about 75:25. In addition, the multicomponent fiber can comprise an elliptical or semi-elliptical core with a center of mass located at about 30% to about 40% of the distance from the fiber's center of mass to its periphery and having a long axis with a length about 1.3 to about 2.8, or about 1.5 to about 2.0 times the length of a short axis of the core.

Methods for making multicomponent fibers are well known and need not be described here in detail. Generally, to form a multicomponent fiber, at least two polymers are extruded separately and fed into a polymer distribution system wherein the polymers are introduced into a segmented spinneret plate. The polymers follow separate paths to the fiber spinneret and are combined in a spinneret hole. The spinneret is configured so that the extrudant has the desired shape.

Following extrusion through the die, the resulting thin fluid strands, or filaments, remain in the molten state for some distance before they are solidified by cooling in a surrounding fluid medium, which may be chilled air blown through the strands. Once solidified, the filaments are taken up on a godet or another take-up surface. In a continuous filament process, the strands are taken up on a godet which draws down the thin fluid streams in proportion to the speed of the take-up godet. In the jet process, the strands are collected in a jet, such as for example, an air gun, and blown onto a take-up surface such as a roller or a moving belt to form a spunbond web. In the meltblown process, air is ejected at the surface of the spinneret which serves to simultaneously draw down and cool the thin fluid streams as they are deposited on a take-up surface in the path of cooling air, thereby forming a fiber web. Regardless of the type of melt spinning procedure which is used, it is important that the thin fluid streams be melt drawn down in a molten state, i.e. before solidification occurs, to reduce the diameter of the fibers. Typical melt draw down ratios known in the art may be utilized. Where a continuous filament or staple process is employed, it may be desirable to draw the strands in the solid state with conventional drawing equipment, such as, for example, sequential godets operating at differential speeds. See, for example, U.S. Pat. No. 5,082,899, incorporated herein by reference in its entirety.

Following drawing in the solid state, the continuous filaments may be crimped or texturized and cut into a desirable fiber length, thereby producing staple fiber. The length of the staple fibers generally ranges from about 25 to about 50 millimeters, although the fibers can be longer or shorter as desired. See, for example, U.S. Pat. No. 4,789,592 to Taniguchi et al. and U.S. Pat. No. 5,336,552 to Strack et al., each of which is herein incorporated by reference in its entirety.

The multicomponent fibers of the invention can be staple fibers, tows, spunbond filaments, continuous filaments, or meltblown fibers. Staple fibers and/or continuous filaments of the present invention particularly may be provided in the form of yarns. In one or more embodiments, fibers formed in accordance with the present invention can have a fineness of about 0.5 to about 100 denier.

As noted above, the multicomponent fibers can be incorporated into a woven or nonwoven fabric. The fibers of the present invention may be formed into fabrics by any means suitable in the art. Fibers other than the multicomponent fibers of the invention may be present as well, including any of the various synthetic and/or natural fibers known in the art. Exemplary synthetic fibers include polyolefin, polyester, polyamide, acrylic, rayon, cellulose acetate, thermoplastic multicomponent fibers (such as conventional sheath/core fibers, for example polyethylene sheath/polyester core fibers) and the like and mixtures thereof. Exemplary natural fibers include wool, cotton, wood pulp fibers and the like and mixtures thereof.

In one or more embodiments, fibers according to the present disclosure may be configured to undergo curling upon the application of heat and/or moisture. As described in U.S. Pat. Appl. Pub. Nos. 2011/0092121 to Kapsali and 2015/0140886 to Kapsali, each of which is herein incorporated by reference in its entirety, a fiber that is an eccentric sheath/core bicomponent fiber has curling capabilities, but in this case, the sheath polymer has a higher natural moisture absorption (regain) than the core polymer. So in humid environments, the sheath polymer swells as it absorbs moisture, while the core polymer does not (or does to a lesser degree). This creates a similar force to that created in the shrinkage case, and because the components are not concentric, the force is resolved by curling the fiber into a helix. However, unlike the fibers that curl because of shrinkage, in this case, lower-humidity environments result in a decrease of moisture in the sheath polymer, leading to reduced swelling and a return to the un-curled state. Accordingly, in this case the curling is reversible.

Woven and nonwoven fabrics which include the multicomponent fibers of the invention as a component are particularly suited for use in apparel that responds to humidity or moisture in order to adjust the breathability of one or more fabrics in the apparel. Specific examples include without limitation athletic apparel (e.g., shirts, jerseys, shorts, pants, etc.), moisture resistant apparel and fabrics (e.g., jackets, shirts, pants, etc.), and sporting equipment (e.g., pads).

In apparel applications, reversibility of the curling characteristics of the fiber is desirable so that a wearer can experience the comfort of a garment whose “breathability” (i.e., air permeability) adjusts continuously to changes in humidity (such as that caused by perspiration). In some applications in which heat-curled fibers are used, reversibility is not desirable and could even be a detriment. An example is a nonwoven fabric that is bulked after formation to form a high-loft nonwoven. By changing the polymer components used in the multicomponent fibers of the present invention, reversible and irreversible curling characteristics can be achieved.

As discussed above, multicomponent fibers according to the present disclosure can be particularly beneficial in providing self-bulking characteristics. The ability to prepare a fiber per the present disclosure that performs suitably in a self-bulking process can be evaluated according to multiple different standards. As such, it is expected that one of skill in the art with the knowledge of the present disclosure can utilize polymer components having characteristics as described herein to form multicomponent fibers that fall within the various standards. The following description is thus provided so that one can clearly evaluate a given fiber in relation to the presently disclosed fibers and should not be construed as limiting the presently disclosed fibers to only specific embodiments.

The fibers of the present invention can be formed into a fabric, typically either by 1) forming a nonwoven fabric using conventional means, 2) forming a continuous filament yarn and weaving or knitting the yarns to form a fabric using conventional means, or 3) forming staple fibers into a spun yarn, which is subsequently knit or woven into a fabric using conventional means. Whichever fabric-forming step is chosen, round fibers of identical polymers and deniers are formed into otherwise identical fabrics, with the only distinguishing factor being the fiber cross section (which may vary in polymer ratio, the cross sectional shape of the core, and/or the position of the core with respect to the center of the fiber).

After forming the fabrics, the fabric samples can be tested according to the test method described in “A Test Method to Determine the Relative Humidity Dependence of the Air Permeability of Textile Materials,” by P. W. Gibson et al, and published in Journal of Testing and Evaluation 25 (4), July, 1997. The performance of each sample can be evaluated on the basis of the degree and direction of change in air permeability between 0% and 98% relative humidity.

EXAMPLE

Using conventional methods known to those familiar with multicomponent fiber extrusion, multicomponent fibers with a circular overall cross section are made in an eccentric sheath/core bicomponent cross section. Four fiber samples are made, each fiber comprising a sheath/core bicomponent fiber with a circular sheath cross section, using nylon 6 as the sheath polymer and polypropylene as the core polymer. All four fiber samples are extruded, drawn, crimped, and cut into staple fibers of identical denier. The fibers are then spun into spun yarns and knit into otherwise identical knit fabrics. For each fabric, the air permeability is measured at various relative humidities using the test method cited above.

In the first sample (sample 1), the polymer ratio is 50:50 by cross sectional area. The polypropylene core has a circular cross section and a center that lies on a radius of the sheath's cross sectional circle separated from the sheath's cross sectional center by 19.0% of the length of the fiber's radius.

In the second sample (sample 2), the polymer ratio is 50:50 and the polypropylene core has a circular cross section with a center that lies on a radius of the sheath's cross sectional circle, separated from the sheath's cross sectional center by 27.5% of the length of the fiber's radius.

In the third sample (sample 3), the sheath:core polymer ratio is 60:40 and the polypropylene core has a circular cross section with a center that lies on a radius of the sheath's cross sectional circle, separated from the sheath's cross sectional center by 27.5% of the radius.

In the fourth sample (sample 4), the sheath:core polymer ratio is 50:50 and the non-circular polypropylene core has a cross section that is approximately circular at the edge nearest the fiber's periphery and approximately elliptical on the side farthest from the fiber's periphery.

The area-weighted center of the polypropylene core's cross section lies on a radius of the sheath's cross sectional circle, separated from the sheath's cross sectional center by 27.5% of the radius. The precise shaping and positioning of the non-circular core can be accomplished by standard means of producing bicomponent fibers, but is facilitated by using appropriately-formed etched plates, as described in U.S. Pat. No. 5,562,930 to Hills, which is herein incorporated by reference.

After testing fabrics made from these four fiber samples, it is observed that the differences in air permeability measured at 98% relative humidity versus that measured at 0% relative humidity is roughly equivalent for samples 2 and 4. The difference in air permeability is a measure of the degree of curl achieved by the fibers in response to humidity. The difference in air permeability (and thus, the degree of curl) for samples 1 and 3 is less than for samples 2 and 4.

While samples 2 and 4 both exhibit similar differences in air permeability (and thus, similar curl), sample 2 is deficient in that the sheath, at its thinnest section, is so thin that in some fibers there is no encapsulation after extrusion, and in other fibers, the thin sheath is breached by the mechanical action of carding and yarn spinning. In some instances, this results in separation of sheath and core, which causes disruptions in fiber processing. As a result, the yarns and fabric made with the sample 2 fibers are made with difficulty. By contrast, the sample 2 fiber has a thicker sheath at its thinnest point, and no breaches of the sheath by the core are observed. As such, the yarn spinning and fabric knitting processes are able to proceed without the difficulties encountered with sample 2 fibers.

Both sample 1 and sample 3 fibers have relatively robust sheath encapsulation of the core at the thinnest area, and thus do not exhibit breaches by the core nor processing difficulties. However, the curling performance of sample 1 and 3 fibers is inferior to that of sample 2 and sample 4 fibers. In summary, sample 4 fibers offer both a maximum curling performance and minimum breaching of the sheath by the core and thus, less processing difficulties.

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. A multicomponent fiber having a sheath/core arrangement, comprising: a sheath component comprising a first polymer component; and a core component comprising a second polymer component; wherein the core component has a first axis that is substantially perpendicular to a second axis, and wherein the first axis is longer than the second axis such that the core component has a non-circular shape; wherein the multicomponent fiber has a first cross-sectional center of mass and a cross-sectional periphery; wherein the core component has a second cross-sectional center of mass; and wherein the second cross-sectional center of mass is positioned from about 20 percent to about 70 percent of the distance from the first cross-sectional center of mass to a point on the cross-sectional periphery.
 2. The multicomponent fiber of claim 1, wherein the fiber is selected from the group consisting of continuous filaments, staple fibers, electrospun fibers, spunbond, and meltblown fibers.
 3. The multicomponent fiber of claim 1, wherein the first polymer component is selected from the group consisting of a polyolefin, a polyester, a polyamide, and mixtures or blends thereof.
 4. The multicomponent fiber of claim 1, wherein the first polymer component is a polyamide.
 5. The multicomponent fiber of claim 1, wherein the second polymer component is selected from the group consisting of a polyolefin, a polyester, a polyamide, and mixtures or blends thereof.
 6. The multicomponent fiber of claim 1, wherein the second polymer component is a polyolefin.
 7. The multicomponent fiber of claim 1, wherein the length of the first axis is about 1.3 to about 2.8 times the length of the second axis.
 8. The multicomponent fiber of claim 1, wherein the core component has a substantially non-uniform, elongated shape.
 9. The multicomponent fiber of claim 1, wherein the core component has a substantially circular side connected to a substantially elliptical side.
 10. The multicomponent fiber of claim 1, wherein the multicomponent fiber has a cross-sectional area comprising about a 40:60 to about a 90:10 ratio of the sheath component to the core component.
 11. The multicomponent fiber of claim 1, wherein the multicomponent fiber has a first cross-sectional center of mass and a cross-sectional periphery, wherein the core component has a second cross-sectional center of mass, and wherein the second cross-sectional center of mass is positioned from about 30 percent to about 40 percent of the distance from the first cross-sectional center of mass to a point on the cross-sectional periphery.
 12. A fabric comprising a plurality of multicomponent fibers according to claim
 1. 13. The fabric of claim 12, wherein the fabric is a knit fabric or a woven fabric.
 14. The fabric of claim 12, wherein the fabric is formed form yarn including one or more of the multicomponent fibers.
 15. A yarn comprising one or more multicomponent fibers according to claim
 1. 16. The yarn of claim 15, wherein the yarn is a spun yarn or a continuous filament yarn.
 17. A method of forming a nonwoven fabric comprising: providing a plurality of multicomponent fibers according to claim 1; and bonding the plurality of multicomponent fibers.
 18. A method of forming a fabric comprising: providing a plurality of multicomponent fibers according to claim 1; and carding, knitting or weaving the plurality of multicomponent fibers to form the fabric.
 19. The method of claim 18, wherein the plurality of multicomponent fibers are in the form of one or both of spun yarns and continuous filament yarns. 